Geographic Range

Leiopelma hamiltoni has a very narrow geographic range, residing only on Stephens Island, New Zealand. Stephens Island lies in the Marlborough Sounds, off of the coast of the South Island of New Zealand. The area of the island is approximately one square mile, but the population resides in a 600 square meter area on the southern tip. Skeletal remains of Hamilton's frog have been found in Waitoma, Hawkes Bay, and Wairarapa on the North Island of New Zealand, indicating that its previous geographic range was much wider. (Newman, 1990; Tocher, 2010; Wang, 2003; "Hamilton's Frog (Leiopelma hamiltoni)", 2007)

Habitat

Hamilton's frogs historically inhabited coastal forests, but are now limited to a 600 square meter, rocky area known as the “frog bank” at the peak of Stephens Island. This area was initially covered with dense vegetation, but was later deforested when grazing farm animals moved into the area. Fortunately, some of the cover was restored after 1951 when a fence was built to keep other animals out of the area. Today, the vegetation consists mainly of grasses and small vines. The many deep crevices within the rock provide a cool, moist, suitable environment for the frog to inhabit during the day. Hamilton’s frogs live in temperatures ranging from approximately 8 °C in the winter to 18°C in the summer. They inhabit elevations around 300 m above sea level.

Physical Description

Hamilton's frogs are mostly brown in color, with a dark brown or black stripe on each side of the head, running the length of the head and passing through the eye. Unlike most frogs which have slit-like pupils, Hamilton's frogs have round pupils. Present on its back, sides, and appendages are visible rows of granular glands that a secrete distasteful fluid when the frog is disturbed by predators. Female frogs are usually larger than males; females have a snout-vent length ranging from 42 to 47 mm while male lengths range from 37 to 43 mm. Like other native New Zealand frogs of the family Leiopelmatidae, L. hamiltoni has ribs that are not fused to vertebrae.

Development

Hamilton's frogs undergo almost all development while in the egg. Development is direct, so tadpoles are not formed. Instead, hatchlings which resemble miniature adults emerge from the eggs. Most froglet features are the same as an adults, except for the temporary tail which eventually is lost. (Bell, 1978; "Animal Fact Sheets: Hamilton's Frog (Leiopelma hamiltoni)", 2006)

Reproduction

Unlike other frogs, Hamilton's frogs do not use calls as a primary method of finding a mate. They lack eardrums as well as vocal chords, so have no way of producing or perceiving calls. Although no calling is done, Hamilton's frog has been known to emit tiny chirps or squeaks during the breeding season.

Like most frogs, the mating posture for Hamilton's frogs is amplexus; a position in which the male grasps the female from behind with his forelegs. Fertilization is external, occurring during amplexus when the male and female are in close contact.

Hamilton's frog breeds once per mating season, sometime between October and December of each year. Eggs are laid in cool, moist places, often under stones or logs that are present on the forest floor. They are laid in multiple strings that tend to clump together. The number of eggs laid usually ranges from seven to nineteen. Each egg has a visible yolk that is surrounded by a clear capsule comprised of three layers: an inner vitelline membrane, a middle gel-like layer, and a protective outer coat.

Once the eggs are laid, it takes approximately 7 to 9 weeks for them to hatch. After hatching, the juveniles spend an additional 11 to 13 weeks completing their development, undergoing such changes as the loss of the tail and further development of the limbs. It takes approximately 3 to 4 years for juveniles to reach sexual maturity. (Bell, 1978; Wang, 2003)

Before fertilization occurs, male frogs seek out and occupy a spot for the female to lay her eggs. Males have been observed to remain at these spots for long periods of time (weeks to months) before the eggs are actually laid. After the eggs are laid, the males stay at the nest and brood. They protect them and maintain a relatively stable environment for them to develop in.

After hatching, the young climb onto the hind legs and backs of the males. Juveniles complete their development here, leaving when the tail has been completely lost and they have reached a snout-vent length of 12 to 13 mm. This male parental care likely serves to keep the young moist, reduce predation, and perhaps reduce fungal infection. (Bell, 1978; "Hamilton's Frog (Leiopelma hamiltoni)", 2007)

Lifespan/Longevity

Although there are no definitive measures of the lifespan of Hamilton's frogs, estimates have been made that they may live to be 23 years old. (Bell, 1994)

Typical lifespanStatus: wild

23 (high) years

Behavior

These frogs do not exhibit any migrational behavior, and it is unknown whether they prefer living in social groups. The entire population lives in close proximity to one another, but this is largely due to habitat availability and does not give any indication to social preferences. (Burton and Burton, 2002)

Hamilton's frog is nocturnal. It emerges at nightfall, and is usually most active on rainy nights with high relative humidity. (Newman, 1990)

Home Range

No information is available regarding home range for Hamilton's frogs.

Communication and Perception

Although it has no vocal chords and cannot call like other frogs, Leiopelma hamiltoni does emit squeaks or chirps in response to predators or during mating. The function of the squeaks during mating is not completely understood, but it is speculated that they might be emitted upon the male release of sperm during mating.

Due to the fact that Hamilton's frogs lack an external eardrum, noise perception is limited to noises with low frequencies. (Bell, 1978; Wang, 2003)

Hamilton's frog uses the specific odors emitted by its feces to communicate with its relatives and other frogs. Chemically, the feces of each frog are somewhat different. Frogs can distinguish relatives from intruders by simply smelling a pile of feces. By defecating in a certain area, frogs are able to claim foraging territories as well as prevent intruders from coming near. If a frog encounters a pile of feces, it can determine the size of the individual who left it and decide whether to stay or flee. (Lee and Waldman, 2002)

Hamilton's frog is a nocturnal species and thus has eyes that are well adapted for seeing in low intensity light. Features of its eye which allow such sight include a high ratio of receptor cells to ganglia, as well as large rod segments and relatively few cone photoreceptor cells. (Meyer-Rochow and Pehlemann, 1990)

Food Habits

Hamilton’s frogs are insectivores, feeding on a wide variety of invertebrates including fruit flies, small crickets, moths, and springtails. Juveniles with a snout-vent length of 20 mm or less lack teeth, and thus are required to eat soft-bodied arthropods like mites and fruit flies.

Predation

Known predators of Hamilton's frogs are native New Zealand tuataras as well as black rats that have been introduced to the area.

Hamilton's frogs exhibit cryptic coloration; its brown and slightly green appearance allows it to camouflage itself among the surrounding rocks, logs and vegetation. When disturbed by predators, it stiffens its body in an attempt to go unnoticed and may remain this way for extended periods of time. These frogs may also take a stiffened, upright stance with legs extended to deter predators. Hamilton’s frogs also secrete a distasteful substance from its granular glands to prevent being eaten by the predator. (Peeling, 2005; Tocher, 2010)

Economic Importance for Humans: Positive

There are no known positive effects of Leiopelma hamiltoni on humans.

Economic Importance for Humans: Negative

There are no known negative effects of Leiopelma hamiltoni on humans.

Conservation Status

Hamilton's frogs are an endangered species according to the ICUN Red List. Recent estimates speculate that there are fewer than 300 individuals left, all of which reside on Stephens Island. Threats to Hamilton’s frogs include predation by native tuataras, as well as introduced mammalian predators like black rats. Although no cases have been reported in L. hamiltoni yet, the species may be susceptible to a deadly fungal disease called chytridiomycosis or chytrid fungus. The disease has been has been acquired by its relative Leiopelma archeyi.

The New Zealand Department of Conservation monitors the population size, and currently has a program in place in attempt to restore it to its former numbers. Efforts to protect the population include building a fence around the "frog bank" to keep predators out, as well as transporting a portion of the population to a nearby island to try and expand its range. (Tocher, 2010)

Contributors

Glossary

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

poisonous

an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

Bell, B. 1994. A review of the status of New Zealand Leiopelma species (Anura: Leiopelmatidae), including a summary of demographic studies in Coromandel and on Maud Island. New Zealand Journal of Zoology, 21: 341-349.

Bell, B. 1978. Observations on the Ecology and Reproduction of the New Zealand Leiopelmid Frogs. Herpetologica, 34/4: 340-354.

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Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.